Compare conditions

Put any two — or three — conditions side by side, adult or pediatric, to spot the look-alike differences fast, row by row.

Septic Arthritis

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In one line

·Bacteria invade the joint space, fill it with pus, and destroy cartilage fast—hours matter.

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Normal physiology

·A healthy joint is a sealed, sterile pocket lined by a thin tissue called the synovium, which makes slippery fluid so the bones glide without grinding. No bacteria live inside.

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What goes wrong

·Bacteria get into the sealed joint space, multiply, and trigger a massive immune attack that fills the joint with pus and destroys the cartilage cushion within hours.

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Hallmark signs

·Hot, red, swollen joint (usually just one)
·Severe pain in the joint that gets worse with any movement
·Not wanting to move or put weight on the joint
·Fever and chills
·The joint looks bigger or puffier than the same joint on the other side
·Warmth when you touch the skin over the joint
·Fast heart rate
·Recent skin infection, IV drug use, or a prosthetic (artificial) joint in the same spot

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Red flags · escalate now

·Fever above 101°F (38.3°C) plus a hot, swollen joint—infection can destroy cartilage in hours
·Refusal to move or bear weight on a joint in a child—especially hip or knee—may be septic arthritis and needs same-day evaluation
·Joint pain plus signs of sepsis: confusion, very low blood pressure, fast breathing, or mottled skin—bacteria may be spreading through the whole body
·Prosthetic (artificial) joint that suddenly becomes painful, warm, or swollen—infection in a fake joint almost always needs surgery to clean out

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Workup

·Joint aspiration (arthrocentesis) — synovial fluid cell count, Gram stain, culture, and crystal exam
·Blood cultures (two sets from separate sites before starting antibiotics)
·Inflammatory markers — ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein)
·Complete blood count (CBC) with differential
·Plain X-ray of the affected joint
·MRI of the joint (if diagnosis is unclear or prosthetic joint is involved)
·Gonorrhea and Chlamydia nucleic acid amplification test (NAAT) from urine or genital swab in sexually active patients

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Treatment

·Urgent sterile joint aspiration (arthrocentesis) BEFORE starting any antibiotics
·Empiric IV antibiotics — vancomycin PLUS either ceftriaxone or cefepime, started immediately after joint aspiration
·Urgent surgical drainage — arthroscopic or open irrigation and debridement of the joint within 24 hours
·Continue IV antibiotics for 2 weeks, then switch to oral antibiotics to complete 4–6 weeks total for native joints (longer for prosthetic joints, osteomyelitis, or MRSA)
·Identify and treat the source of bacteria — remove infected IV lines, drain skin abscesses, treat endocarditis, address IV drug use wounds
·Remove or revise prosthetic joint implant if infection does not clear with DAIR (debridement, antibiotics, and implant retention) within 2 weeks or if infection is chronic
·Pain control with acetaminophen or NSAIDs (ibuprofen, naproxen) and physical therapy once acute infection is controlled

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NCLEX trap

·Start IV vancomycin plus ceftriaxone immediately — before any culture results — and tap the joint first to grab fluid for proof. Waiting even a few hours lets bacteria chew through cartilage and can lead to sepsis. The rule: tap, then treat, then wait for cultures.
·Some patients, especially kids, have little or no fever even with a joint full of bacteria. The hot, swollen, immovable joint is your red flag — fever or no fever, tap the joint and treat it urgently. Fever is helpful when present but never required to make the diagnosis.
·Antibiotics alone cannot clean out thick pus, dead white cells, and chunks of damaged tissue. Most septic arthritis needs urgent arthroscopic or open lavage — surgeons rinse the bacteria out of the joint space — plus IV antibiotics. Both together save the joint; antibiotics alone often fail.
·Blood culture is negative in many septic arthritis cases because bacteria may stay inside the joint and never spill into blood. The joint fluid culture is the real proof. Always send both, but never wait for blood culture results before acting — the joint fluid tells the story.
·X-ray is slow and misses early septic arthritis — bone damage takes days to weeks to show up on film. Tap the joint now. Ultrasound can guide your needle if you cannot see or feel fluid clearly, and send the fluid for culture and Gram stain today. X-ray can wait; the tap cannot.
·Prosthetic joint infection needs much longer antibiotics — usually 6 weeks IV, then several more weeks or months by mouth — and often surgical removal or exchange of the implant. Infectious disease specialists should help manage it. Natural joint septic arthritis is typically 2 weeks IV plus 2 to 4 weeks oral — much shorter and simpler.

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